I scanned Tor starting Friday April 11th and ended Sunday April 13th. I stopped cause I got enough evidence on leaked plain text.
I wasn't sure what to do with the data so I was sitting on it for a couple of days but than decided to just blog about it.

Update:

Tor doesn't have too many exitnodes, the nodes I was testing are Tor nodes in general not only exitnodes. Never the less I found
a number of vulnerable exitnodes that leak plain text data.

Tuesday April 7th I started my own investigations of the Heartbleed issue. In this blog post I want
to talk about one of the things I've been looking into that is the effect heartbleed has on TOR.
TOR heavily uses SSL to encrypt traffic between the various TOR nodes. TOR was obviously vulnerable as reported by the TOR project.

For my investigation I pulled a list of about 5000 TOR nodes using dan.me.uk. Using one of the many proof-of-concept
exploits I scanned the TOR nodes to determine if they are vulnerable. I found 1045 of the 5000 nodes to be vulnerable to the heartbleed bug, that is about 20%.

I briefly checked the leaked memory to determine if plain text is leaked that is related to TOR user traffic. Yes, TOR exitnodes that are vulnerable to heartbleed
leak plain text user traffic. You can find anything ranging from hostnames, downloaded web content, to session IDs, etc.

The majority of the vulnerable TOR nodes are located in Germany, Russia, France, Netherlands, United Kingdom, and Japan. The TOR network has more than
5000 nodes so this is not a complete picture but it provides a good overview of the possible number of vulnerable exitnodes.

The heartbleed bug basically allows any one to obtain traffic coming in and out of TOR exitnodes (given that the actual connection that is run over TOR is
not encrypted itself). Of course a malicious party could run a TOR exitnode and inspect all the traffic that passes thru it, but this requires
running a TOR node in the first place. Using the heartbleed bug anyone can query vulnerable exitnodes to obtain TOR exit traffic.

There are a number of possible solutions for this problem. 1) update vulnerable TOR nodes (hopefully in progress), 2) create a blacklist of vulnerable TOR nodes and
avoid them, 3) stop using TOR until all nodes are updated.

Further Steps:

Scan all TOR exitnodes to create a black list of vulnerable nodes so users can avoid them.

Notes:

One interesting thing I found is the large number of requests that seem to be originating from malware due to the domain names looking like the output of a DGA.